The idothyronine derivatives 3,5,3'-triiodothyronine (T3) and thyroxine (T4) are important for metabolic regulation. Although the relationships between thyrominetic activity and drug structure have been extensively studied, there is still a wide gap in our knowledge of the equilibrium conformations of these materials and how conformation is related to activity. A similar situation exists with the beta-adrenergic agents. Nuclear magnetic resonance - lanthanide shift reagent (NMR-LSR) technique to determine the solution conformations of analogs of the thyrominetic and adrenergic agents, and these data will be studied to identify possible structure-conformation activity relationships. The NMR-LSR method has a great potential for conformational analysis, but is generally usable only when the target molecule possesses a single LSR complexation site. Our investigation of the thyronine analogs utilizes a conformationally flexible substituent linked to a (2.2.1)-bicyclic amide, which contains only one LSR site. However, for molecules with several potential binding sites, new techniques employing a series of "super complexing agents" will be developed for the determination of the solution conformations of these materials, and the methods will be used to study the adrenergic analogs.